Method for controlling thin film growth of compound semiconductors using mass spectrometer detectors

Abstract

A molecular beam epitaxy (MBE) system (10) is provided to grow thin film, epitaxy layers (44, 46, 48, 50) on compound semiconductor substrates (40). A mass spectrometer detector (95) is used to monitor and control the flux from selected sources (21, 23, 25, 27) within the MBE system (10). A uniform layer of indium gallium arsenide (46, 50) may be grown on a semiconductor substrate (40) by controlling the indium flux with respect to substrate (40) temperature and time. An epitaxy layer (46) of indium gallium arsenide with uniform mole fraction concentration and reduced lattice strain is produced.

What is claimed is: 
     
       1. A method for growing thin film layers on a compound semiconductor wafer within a molecular beam epitaxy chamber, said method comprising the steps of: heating said wafer to a selected temperature;   directing the flux from a plurality of atomic and/or molecular sources onto said semiconductor wafer; and   varying said flux from one or more of said sources and the temperature of said wafer based on information from one or more mass spectrometer detectors which receive input from the surface of said wafer.   
     
     
       2. The method for growing thin film layers as defined in claim 1 further comprising the steps of heating each source to a selected temperature to produce the desired atomic flux from each source. 
     
     
       3. The method of claim 2 and further comprising the step of changing the temperature of one or more sources in response to information from said mass spectrometer detector. 
     
     
       4. The method of claim 1 wherein said mass spectrometer detector detects indium. 
     
     
       5. The method of claim 1 further comprising the steps of: monitoring the chamber for indium with said mass spectrometer detector; and   varying the flux from an indium source to correspond with changes in said wafer temperature.   
     
     
       6. A method for growing epitaxy layers on a gallium arsenide substrate comprising the steps of: placing the gallium arsenide substrate on a substrate holder within a molecular beam epitaxy (MBE) system;   placing a plurality of atomic and molecular sources within said MBE system;   placing a mass spectrometer detector within said MBE system;   heating said gallium arsenide substrate to a selected temperature;   directing the flux from one or more of said sources onto said gallium arsenide substrate;   monitoring said mass spectrometer detector for atomic signals associated with a selected source; and   varying the flux from said selected source and the temperature of said substrate based on information from said mass spectrometer detector.   
     
     
       7. The method for growing epitaxy layers as defined in claim 6 further comprising the steps of heating each source to a selected temperature to produce the desired flux from each source. 
     
     
       8. The method for growing epitaxy layers as defined in claim 7 further comprising the step of changing the temperature of the selected source in response to information from the mass spectrometer detector. 
     
     
       9. The method for growing epitaxy layers as defined in claim 6 further comprising the step of monitoring the chamber for indium by setting the mass spectrometer detector for signals having 115 atomic weight units. 
     
     
       10. The method for growing epitaxy layers as defined in claim 6 further comprising the steps of: growing a buffer layer of gallium arsenide on a gallium arsenide substrate;   growing an indium gallium arsenide epitaxy layer on the gallium arsenide buffer layer; and   growing a thin cap layer of gallium arsenide or aluminum gallium arsenide on the indium gallium arsenide epitaxy layer.   
     
     
       11. The method for growing epitaxy layers as defined in claim 6 further comprising the steps of: growing an epitaxy layer of indium gallium arsenide on gallium arsenide; and   growing a thin cap layer less than twelve angstroms thick of gallium arsenide or aluminum gallium arsenide on the indium gallium arsenide epitaxy layer.   
     
     
       12. The method for growing epitaxy layers as defined in claim 6 further comprising the step of positioning the mass spectrometer detector to receive reflected signals from the surface of the gallium arsenide substrate.